The trend towards smaller available feature sizes in integrated circuit processes enables systems and circuits operating at ever higher frequencies. As a result, research and commercial interests are moving towards circuits and systems operating in the millimeter- and sub-millimeter wave regions using standard integrated circuit technologies to provide less expensive and mass-producible solutions compared to discrete designs.
Advances in packaging and thin film technologies allow the integration of several integrated circuit dies or components, possibly from different technologies or processes, into integrated systems offering solutions in small form factors. Examples of such systems include integration of processing units with cache memory integrated circuit dies in a stacked configuration for thin form factor packages, or integration of RF input or output amplification stages with off-chip surface acoustic wave filters on a ceramic substrate.
Among others, current areas of interest include radio circuits and systems, sensors, continuous and pulsed power sources, imaging systems and spectroscopic equipment operating at millimeter and sub-millimeter wavelengths, sometimes also referred to as the terahertz or far-infrared regime. In the millimeter-wave region, applications for integrated receiver and transmitter systems include car radar, communications systems and imaging systems for personal and property security among others. In the sub-millimeter wave region, so-called terahertz electronics is actively researched with applications either envisioned or already marketed for terahertz spectroscopy, short-distance communication, and medical and process control imaging among others.
In all of the above cases, it is desirable to migrate, whenever possible, towards commodity technologies (e.g. CMOS versus hetero junction bipolar technologies) and higher levels of integration to reduce costs, increase functionality and potentially open new markets. As part of this drive, it is highly desirable for millimeter- and sub-millimeter systems to integrate as much as possible all components such as transmit and receive antennas and electromagnetic sensors. One of the difficulties encountered is to control the electromagnetic near- and far-fields as the wavelengths become comparable to the physical dimensions of the circuit and electromagnetic energy couples to the bulk and surrounding dielectric (air) or has to be contained to the surface. This, in turn, makes it difficult to implement truly versatile, broad-band and efficient microelectronic circuits in these frequency ranges.
Traditionally, integrated circuits are planar, that is they are formed using process layers on the surface of a semiconductor substrate. The substrate is then packaged using one of many packaging options. In this context, the terms “antenna”, “element” or “electromagnetic element” are typically understood to mean any circuit element electromagnetically interacting with the physical environment. FIG. 1A illustrates a typical system package that involves attaching an integrated electromagnetic element to a ground plane. The package 10 includes an integrated electromagnetic element 12 on a substrate 14 with a package ground-plane 16. The substrate connects to external devices via wire bonds 18 and package leads 20. A flip-chip packaging solution is illustrated in FIG. 1B. The flip-chip package 30 also includes an integrated electromagnetic element 32 on a substrate 34 that connects with external devices via solder bumps 36 and ball pins 38. Other packaging implementations are also possible, but all of these share the planar nature of the electromagnetic elements due to the planar nature of semiconductor processing.
In all of the implementations described above, trade-offs can exist because electromagnetic boundary conditions are imposed in a thin, effectively planar region (within the thickness manipulated by the process). In particular, with the antennas and electromagnetic elements constrained to a thin region in space, trade-offs exist with respect to efficiency, versatility and usable range of operation frequencies when attempting to manipulate the electromagnetic environment. Versatility refers to the ability to reconfigure the antenna. An example of a reconfigurable antenna system is a phased array, where electronic reconfiguration achieves directionality. Broad-band operation, meaning that the antenna can operate over a wide range of frequencies is typically desirable, because it allows greater freedom in system design and also lowers the overall risk of malfunction as narrow-band antennas are typically more susceptible to process and environmental changes.